GHSA-8643-3wh5-rmjq is a medium-severity (CVSS 5.3) CWE-347 vulnerability. A fix is available — see the affected versions and patch details below.
libgit2 fails to verify SSH keys by default
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8643-3wh5-rmjq.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-8643-3wh5-rmjq plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Description
libgit2 is a cross-platform, linkable library implementation of Git. When using an SSH remote with the optional libssh2 backend, libgit2 does not perform certificate checking by default. Prior versions of libgit2 require the caller to set the certificate_check field of libgit2's git_remote_callbacks structure - if a certificate check callback is not set, libgit2 does not perform any certificate checking. This means that by default - without configuring a certificate check callback, clients will not perform validation on the server SSH keys and may be subject to a man-in-the-middle attack. Users are encouraged to upgrade to v1.4.5 or v1.5.1. Users unable to upgrade should ensure that all relevant certificates are manually checked.
Detection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`). Because exploitation targets the running service rather than your application code, O3 also flags the exploit behaviour from runtime telemetry and egress traffic.
Fix
Upgrade the affected component to the fixed release for GHSA-8643-3wh5-rmjq, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
Reduce reachability while you patch: restrict network access to the service to trusted sources, disable or gate the affected component where your deployment allows it, and add a WAF/IPS signature if one exists for GHSA-8643-3wh5-rmjq. O3's runtime protection blocks the cwe-347 flaw at execution, which holds the line on hosts you cannot patch immediately.
How O3 protects you
O3 detects and blocks GHSA-8643-3wh5-rmjq exploitation at runtime with eBPF exploit-chain detection, plus L7 egress monitoring that catches a post-exploitation callback and cuts the attacker's outbound channel.
Tailored to GHSA-8643-3wh5-rmjq. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is GHSA-8643-3wh5-rmjq in your dependencies?
O3 Security finds GHSA-8643-3wh5-rmjq across dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.